Keeping stem cells under control: New insights into the mechanisms that limit niche-stem cell signaling within the reproductive system.

Adult stem cells reside in specialized microenvironments, called niches, that maintain stem cells in an undifferentiated and self-renewing state. Defining and understanding the mechanisms that restrict niche signaling exclusively to stem cells is crucial to determine how stem cells undergo self-renewal while their progeny, often located just one cell diameter away from the niche, differentiate. Despite extensive studies on the signaling pathways that operate within stem cells and their niches, how this segregation occurs remains elusive. Here we review recent progress on the characterization of niche-stem cell interactions, with a focus on emerging mechanisms that spatially restrict niche signaling. Mol. Reprod. Dev. 83: 675-683, 2016